That comes and goes when cutting certain types grasses. This results in hand numbness, stress on gearhead and uneven wear on blades.
Cause
This is the result of grass being sucked in between the top and bottom hubs, due to the fan effect of the Anti-Fouling Blades and building up on the leading edge of the Anti-Fouling Blades.
This in itself was to so much a problem; it was the build-up of grass on one of the Anti-Fouling Blades being dragged away by the centrifugal forces, resulting in a slight imbalance and vibration. Grasses would again start to build up, but before it evened out, one of the other build ups would break away.
Solution
I tried a number of solutions to try and resolve this problem, increasing the length of the front internal leading edge, making a sharp pointed leading edge, sharpening the leading edge to a razor edge and reversing the hubs so that the top was on the bottom and the bottom was on the top. None of these made any improvement and in some cases made it worse.
The only thing that made any improvement was when I reduced the space between the hub plates by removing the spacer washers and reducing the gap form 7mm down to 3mm.
The smaller gap between the hubs created less suction between the hubs and even though grass still gets stuck of the front edge of the Anti-Fouling blades, it stays there and does not break away.
As usual, this improvement created another problem, so I had to modify the design of the hubs to guide the Flail-Blade as they are knocked backwards at very high speeds to prevent a flexing blade from cutting into the hubs, like with an earlier problem discussed above.
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